Floating platform with storage tanks for compressed gas and/or hydrate forms of hydrocarbons

ABSTRACT

A floating platform to provide fluid separation and storage of hydrocarbon effluents and the like. The platform includes a floating hull structure with a hollow central section and a center assembly mounted within the hollow central section and being retractable and extendable below the hull. A floating platform is described wherein fluid separators and/or storage vessels are disposed within the floating hull to provide additional separation capacity. The floating hull may also house ballast tanks and liquid storage tanks. Additionally, fluid separators may be housed within the central section.

BACKGROUND OF THE INVENTION

[0001] This application is a continuation-in-part of U.S. Patentapplication Ser. No. 09/980,844 filed Oct. 22, 2001.

[0002] 1. Field of the Invention

[0003] The invention relates generally to offshore platforms and buoyswith hull based separator and storage vessels and tanks for containmentof hydrocarbon gases and their hydrate forms.

[0004] 2. Description of the Related Art

[0005] Deepwater oil discoveries of hydrocarbons coupled with longdistances to pipeline infrastructure cause small amounts of associatedgas to be an increasing limitation to obtaining offshore domesticenergy. Present solutions require installing extensive pipelines inincreasingly deep water with very high capital expenditures thatfrequently prevent projects from going forward, increasing foreign oilimport. Solutions in the past allowed reinjection of gas, although thisis now not considered a responsible natural resource by operators.

[0006] Regulations in the interest of gaining the maximum value fromnatural resources and heightened environmental awareness, limit flaring,venting and re-injection of gas and give rise to the necessity of deepwater offshore gas compression with storage and transit to the marketwithout pipelines when they are cost prohibitive.

[0007] A solution to this issue would be to utilize economic floatingplatforms to collect, separate water and condensate, and store thehydrocarbon gas in a pressurized and/or cooled state for transfer bysimilar means as a mobile shuttle vessel. This approach is commonly usedfor storage and shuttling of oil around the world via floating storageand offloading vessels termed FSO's or FPSO's with processing facilitiesas well. Transit ships for compressed natural gas (CNG) storage havebeen proposed and are being planned. However, the implementation of afixed floating platform for storage of CNG has not been addressed in themarketplace. A related need is for a platform or facility that permitsstorage of the solid form of hydrocarbon gases, or their hydrate form assolids, within a floating platform.

SUMMARY OF THE INVENTION

[0008] The present invention provides an offshore floating facility forstorage of hydrocarbon gas under controlled pressure and temperatureand/or for storage of the hydrate form of hydrocarbons gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For further understanding of the nature and objects of thepresent invention, reference should be had to the following drawings inwhich like parts are given like reference numerals and wherein:

[0010]FIG. 1 presents an elevation view of a floating vessel inaccordance with the present invention.

[0011]FIG. 2 is an elevation view (partially cut-away) of the vesselshown in FIG. 1.

[0012]FIG. 3 is a detail view depicting an exemplary temperature controlsystem for a storage vessel in accordance with the present invention.

[0013]FIG. 4 is a block diagram illustrating steps in an exemplarystorage method in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] PCT international application serial number PCT/US00/10936,entitled “Satellite Separator Platform” describes a floating vesselhaving a floating hull structure with a center column assembly that isextendable and retractable with respect to the hull structure.PCT/US00/10936, which is owned by the assignee of the present invention,is hereby incorporated herein by reference. That application describesthe use of fluid separators within the center column assembly of theplatform. In accordance with the present invention, there are providedmeans within the floating hull as well as atop the hull for storage ofcompressed gases and solid hydrates. Additionally, such storage may beprovided within the center column assembly.

[0015]FIG. 1 depicts a floating vessel 100 having a floating hullstructure 102 and a center column assembly 104. The center columnassembly 104 is retained within a hollow central section 103 (in FIG. 2)and is axially moveable with respect to the hull 102 so that the centercolumn assembly 104 is extendable and retractable below the hull 102.The center column assembly 104 preferably includes a plurality oflongitudinal fluid separators 105 for separation of fluid componentsfrom a fluid mixture. The separators 105 may be gravity-type separatorsor hydrocyclone separators. The hull 102 presents an upper deck 106 forthe support of a crane (not shown), a helipad (not shown) and otherequipment useful for operation of the platform 100. Deck-mountedvertically-disposed storage vessels 200 and horizontally-disposedstorage vessels 201 are shown supported upon the upper deck 106.

[0016] The elevation view provided by FIG. 2 reveals storage vessels 202within the hull 102 for containing hydrocarbon gases and/or hydrates. Itis currently preferred that the floating vessel 100 be used fortemporary storage of compressed natural gas and/or solid hydrocarbonhydrates. The storage vessels 202 provide storage and/or separation ofthe hydrocarbons. The storage vessels 202 may extend above the deck 106,as well. The storage vessels 202 may further be provided with anenvironmental boundary 300, as shown in FIG. 2, to improve thevolumetric or separation efficiency of the vessels 202. Theenvironmental boundary 300 is provided by a shell or jacket ofprotective insulation. Within the environmental boundary 300, thetemperature of the contents of the vessels 202 would be controlledwithin a desired range. Insulation and other measures for temperaturecontrols are provided. The outer surface of the vessels 202 are designedto include insulation methodology to reduce the transfer of heat to orfrom the surrounding seawater 204, hull 102, and deck 106 to thecontained hydrocarbon gas or hydrates. FIG. 3 illustrates, in schematicfashion, an exemplary temperature control system for the storage vessel202 within the environmental boundary 300. A heated/cooled fluid 302surrounds the storage vessel 202. An operably associatedcontroller/heating-cooling/fluid replenishment/pressure control system304, of a type known in the art, controls the heating/cooling coil 302to maintain the storage vessel 202 and its contents at or near apredetermined temperature and pressure, based upon readings from sensor305. The controller 304 also provides for replenishment and circulationof fluid 302 within the environmental boundary 300 via entry and returnpiping 303, 307. Although FIG. 3 only shows the temperature controlarrangement with respect to vessel 202, it should be understood thatsuch may be used for all such storage vessels of the platform 100.Temperature control is important in the instance of hydrates to ensurethat they do not sublimate and for gases, to ensure that they remain intheir gaseous form.

[0017] Embodiments of the present invention provide for an offshorefloating structure with separators and/or storage vessels forcontainment and control of gaseous or hydrate forms of hydrocarbons ineither the center column assembly 104, within the hull 102, or upon thedeck 106 of the hull 102. The systems and methods of the presentinvention provide for temporary or interim storage of hydrocarbon gasesand solid hydrates following production from a well and prior tooffloading and transport by transport tanker (not shown) to a remotelocation. In operation, a floating platform, such as platform 100 ispositioned proximate a hydrocarbon production facility, such as anoffshore well platform (not shown). It is then moored in place. FIG. 4illustrates steps for a method of storing CNG/hydrates upon the platform100. Produced hydrocarbon hydrates and/or CNG is then transmitted to theplatform 100 via hoses and other conduits (not shown) of a type known inthe art (step 306). These materials are then stored within storagevessels 200, 201, 206 or 202 (step 308). Temperature is controlled forthe storage vessel during storage of the materials (step 310). Finally,the materials are offloaded to a transport tanker (step 312).

[0018] Additionally, temporary/interim storage of hydrocarbon gasesand/or solid hydrates may be accomplished within the context of thepresent invention within floating platforms having designs other thanthat of the floating vessel 100 described above. The solution ofeffective CNG or hydrate storage in a moored vessel for purposes ofenabling CNG or hydrate transfer from the originating hydrocarbonsources (i.e., subsea wells) or at the market end can be achieved withmany forms of fixed and floating vessels.

[0019] In addition, the platform 100 may provide for storage ofhydrocarbon gases and/or solid hydrates within the center columnassembly 104. FIG. 2 illustrates storage vessel 206 within the centercolumn assembly 104.

[0020] The best mode and preferred embodiments of the invention havebeen described. It is to be understood that the invention is notlimited, thereto, but rather is to be measured by the scope and spiritof appended claims.

What is claimed is:
 1. A floating structure comprising: a floatable hullthat presents an upper deck; and a storage vessel for storage of amaterial of the group consisting of hydrocarbon gas and solidhydrocarbon hydrates.
 2. The floating structure of claim 1 wherein thestorage vessel is disposed within the floatable hull.
 3. The floatingstructure of claim 1 wherein the storage vessel is located atop thefloatable hull.
 4. The floating structure of claim 1 wherein the storagevessel is surrounded by an environmental boundary.
 5. The floatingstructure of claim 4 wherein the environmental boundary comprises aninsulated shell.
 6. The floating structure of claim 1 wherein thestorage vessel is disposed within a center column assembly of thefloating structure.
 7. The floating structure of claim 4 whereintemperature is controlled within the environmental boundary.
 8. Thefloating structure of claim 7 wherein temperature is controlled viacirculation of a fluid of desired temperature within the boundary. 9.The floating structure of claim 8 wherein fluid pressure of the fluid isalso controlled.
 10. A floating structure comprising: a floatable hullthat presents an upper deck and defines a hollow central sectiontherewithin; a center assembly mounted within the hollow central sectionand being retractable and extendable below the hull; and a plurality ofstorage vessels disposed within the floatable hull, each of the storagevessels being useful for storage of hydrocarbon gas or hydrates.
 11. Thefloating structure of claim 10 wherein at least one of the storagevessels is located upon the upper deck.
 12. The floating structure ofclaim 10 wherein at least one of the storage vessels is located withinthe floating hull.
 13. The floating structure of claim 10 wherein atleast one of the storage vessels is located within the center columnassembly.
 14. A method of storing compressed hydrocarbon gases or solidhydrates following production and prior to transport to a remotelocation, comprising the steps of: disposing said gases or hydrateswithin a storage vessel upon a floating platform; controlling thetemperature of the storage vessel.
 15. The method of claim 14 furthercomprising the step of offloading the gases or hydrates to a transporttanker.
 16. The method of claim 14 further comprising the step ofmooring the floating platform in place proximate an offshore productionwell prior to disposing the gases or hydrates within the storage vessel.17. The method of claim 14 wherein the step of controlling thetemperature of the storage vessel comprises circulating a fluid ofdesired temperature about the storage vessel.